1. Field of the Invention
The present invention relates to an electric rotary machine (hereinafter referred to as xe2x80x9crotary machine,xe2x80x9d or occasionally xe2x80x9cmotorxe2x80x9d as appropriate), and more particularly to a radial gap type rotary machine comprising an armature with independent salient poles.
2. Description of the Related Art
In a conventional rotary machine including an armature structured such that a plurality of ring-shaped yoke pieces, which are made of a soft magnetic plate, such as a silicon steel plate, and which each have a plurality of pole tooth portions protruding radially, are stacked in the axial direction, since each of the ring-shaped yoke pieces is punched out integrally with the plurality of pole tooth portions as a single piece (the armature composed of the ring-shaped yoke pieces thus structured is hereinafter referred to as xe2x80x9cintegral armaturexe2x80x9d as appropriate), pole teeth each composed of a stack number of pole tooth portions are not partitioned structurally and therefore a resultant armature will have superior magnetic efficiency (low reluctance). However, in a small rotary machine, since a wire is usually wound directly on the pole teeth, the integral armature makes the winding operation troublesome, and extremely troublesome when the rotary machine is of inner rotor type. As a result, the winding operation takes a long time, and the winding incurs unsatisfactory space factor as well. And, due to the flyer-winding involved in this case, the wire is subject to torsional stress during the winding operation, thereby failing to ensure reliability of the winding area.
Under the circumstances above described, a rare earth magnet having high energy product has been developed recently, and the structure of a rotary machine can be reviewed by means of magnetic circuit analysis using a computer. This works to enable a rotary machine with an armature of discrete salient pole structure (this armature is hereinafter referred to as xe2x80x9cdiscrete armaturexe2x80x9d as appropriate) to obtain requisite motor characteristics. The rotary machine with the discrete armature may give some undesired increase in reluctance but offers great advantages of easier winding operation and increased space factor of winding so as to override the disadvantageous increase in reluctance. From this, it is now realized that the rotary machine with the discrete armature produces higher performance and is manufactured less expensively on the whole, and there is a growing demand for the discrete armature.
One example of the discrete armature is manufactured such that pole tooth portions are dismembered off its main body portion of an integral armature, a wire is wound around each of the dismembered pole tooth portions thereby constituting each salient pole portion, and that the pole tooth portions each with a wire wound therearound, namely, the salient pole portions are rejoined to the main body portion by laser-welding, or the like.
The armature thus structured, however, has a disadvantage that the integral armature has to be first sectioned and later reassembled, thereby requiring an additional time. Also, when the pole tooth portions each with a winding (namely salient poles) are rejoined to the main body portion, the stack layers of the both portions have to be matched with each other, and therefore it is required that respective portions be held together by a well-maintained tool and surely welded plate by plate for ensuring precision, which results in decreased workability. And, joints (welded portions) deteriorate significantly in mechanical strength and magnetic characteristics.
To overcome the above described problems, the present inventors disclosed in Japanese Patent Application Laid-open No. 2001-238377 a radial gap type rotary machine comprising: a discrete armature including a plurality of discrete salient poles and a cylindrical pole tooth ring for positioning and fixing the salient poles, thereby connecting the salient poles to one another magnetically and mechanically; and a cylindrical stator ring adapted to decrease leakage flux resulting from magnetic discontinuity.
FIG. 1 shows a pole tooth ring 150 of the rotary machine disclosed in the above mentioned Japanese Patent Application Laid-open No. 2001-238377. The pole tooth ring 150 is of a soft magnetic steel plate and is produced, for example, by the process of drawing. The pole tooth ring 150 has six slits 150a shaped substantially rectangular, extending axially (in parallel to a shaft of a rotor) from its one axial end beyond its halfway point and arrayed circumferentially at even intervals. The slits 150a do not necessarily have to be arrayed at even intervals.
Pole teeth of salient poles are fitted into respective slits 150a, whereby the salient poles are appropriately positioned. And, a stator ring made of a steel plate in a hollow-cylindrical configuration is disposed over the pole tooth ring 150, thereby forming a magnetic circuit.
The rotary machine disclosed in the above Japanese Patent Application Laid-open No. 2001-238377 has the following problem. The slits 150a are produced by punching, so their width is determined to the dimension of the punching die and comes out with very little variation. On the other hand, the pole teeth to be fitted into the slits 150a are produced by stacking magnetic steel plates, and the thickness of each of the plates stacked adds up to the thickness of the pole tooth, thus the variation of the pole tooth thickness can be as large as the variation of one plate thickness multiplied by the stack number. Accordingly, it can happen that the condition of contact between the side wall of the slit 150a and the pole tooth is not kept constant.
For example, in case of a rotary machine with a diameter of 42 mm, the variation of the slit width is xc2x10.03 mm, while the variation of the pole tooth thickness is gained by multiplying xc2x10.02 mm (the variation of each plate with a thickness of 0.5 mm) by 7 (the stack number) amounting to as large as xc2x10.14 mm. This large variation sometimes makes it impossible for the pole tooth to fit into the slit, or causes the pole tooth to make unstable contact or even no contact with the side wall of the slit with regard to the slit width direction.
If the pole tooth does not make stable contact with the side wall of the slit, that is, with the pole tooth ring, the magnetic circuit at the stator is not stable, thereby causing the rotary machine to rotate unstably generating vibrations and noises. This renders the rotary machine unsuitable for precision instruments.
The present invention has been made in view of the above described problems, and its object is to provide a rotary machine, in which a stable contact is ensured between a pole tooth ring and pole teeth thereby obtaining stable motor characteristics.
In order to achieve the above object, according to a first aspect of the present invention, a rotary machine comprises: a pole tooth ring provided with a plurality of slits; and a plurality of salient poles each including a pole tooth, and each positioned and fixed such that the pole tooth is fitted into the slit adapted to be elastically deformed when receiving the pole tooth fitted thereinto.
According to a second aspect of the present invention, in the rotary machine of the first aspect, the slit is configured so as to generate elasticity acting against the pole tooth fitted into the slit.
According to a third aspect of the present invention, in the rotary machine of the second aspect, the elasticity is generated by means of at least one opening provided along at least one side wall of the slit and resultant wavy portion of the at least one side wall.
According to a fourth aspect of the present invention, in the rotary machine of the second aspect, the elasticity is generated by means of at least one opening provided along one side wall of the slit and continuous with the slit.
Accordingly, in the rotary machine of the present invention, when the pole tooth is fitted into the slit, the variation of the pole tooth thickness can be absorbed by the elasticity provided at the side wall of the slit, whereby a stable contact is ensured between the pole teeth of the salient poles and the side wall of the slit, that is, the pole tooth ring, and therefore a stable magnetic circuit is formed ensuring stable motor characteristics.